Three areas of research will be pursued in the coming year. (a) We will continue to investigate the effect of stabilizing or destabilizing the helix on the error frequency in DNA synthesis. (b) Mut D will be investigated to see what factor causes the reduced fidelity of DNA synthesis in plasmolyzed cells and is also presumably involved in the markedly reduced rate of DNA synthesis in plasmolyzed cells. This is of especial interest because mapping experiments have placed the Mut D locus outside of the known DNA polymerase. (c) A Pol III mutator polymerase in E. coli will be purified and characterized in respect to its defect in synthesizing correct DNA.